The present invention relates to magnetic tape cassettes, and more particularly to an improved video tape cassette.
A typical example of a heretofore known audio tape cassette is a compact cassette made by Phillips Co. and a typical example of a known video tape cassette is a beta format or video home system (VHS) type cassette.
A video tape cassette must have a considerably better and more stable tape running characteristic than an audio tape cassette. In addition, magnetic tape used in a video cassette must be capable of being recorded at a higher recording density and must have a significantly better electromagnetic conversion characteristic than an audio cassette. Accordingly, the possible reduction of the width of a video tape cassette has been limited. The size and weight of presently available video tape cassettes are greater than what is desired.
On the other hand, as magnetic tape and as video recording and reproducing devices have been improved in performance recently, there has been a strong demand for the provision of a portable video system which is more easily portable than a conventional fixed position type video system and which can be used outdoors. This makes it necessary to reduce the size and weight of the video tape cassette.
However, in decreasing the size and weight of the video tape cassette (hereinafter referred to merely as "a cassette"), because of the inherent structural limitations of the cassette, problems remain concerning how to maintain unchanged or improve the running of the magnetic tape, the loading of the magnetic tape in the recording and reproducing device, or the like and how to decrease the manufacturing cost.
FIG. 1 is a plan view showing an example of the arrangement of a tape transport structure in a conventional miniaturized magnetic tape cassette. A pair of hubs 2 and 3 around which a magnetic tape T can be wound are disposed respectively at the right-hand and left-hand sides in the hollow interior of a cassette casing 1. The magnetic tape T between the hubs 2 and 3 passes along tape running paths which are defined by a plurality of guide pins and/or guide rollers 5 which are provided on both sides of a front opening 4 in the cassette casing 1. A turnable cover 7 is pivotally supported on both sides of the cassette casing 1. After the turnable cover 7 is opened, the magnetic tape T loaded across the front opening 4 is pulled out of the front opening 4 with a pulling member provided in the recording and reproducing device so that the recording or reproducing operation can be carried out. To accurately guide the tape along the tape running paths by suppressing shifting of the tape in its widthwise direction in the tape running paths, pad members 6 are provided which press the magnetic tape T against the above-described guide pins or rollers 6 under a substantially constant pressure at all times.
Since the space in the above-described small magnetic tape cassette is limited, it is difficult to provide in the cassette not only a locking mechanism for the turnable cover 7 but also a mechanism for maintaining the turnable cover 7 closed. Even if a space for providing such mechanism were forcibly made available in the cassette, it would be necessary to miniaturize the components forming these mechanisms and accordingly the efficiency of assembling the cassette would be greatly decreased. In these points, the conventional small magnetic tape cassette is disadvantageous.
FIGS. 2 and 3 show an example of a turnable cover locking mechanism 20 which is employed extensively in a conventional normal size cassette which has a relatively larger amount of available space in it. This locking mechanism 20 shown in FIGS. 2 and 3 includes an L-shaped locking lever 22 which is rockable around a shaft 21 which extends upwardly from the inside bottom 1b of the cassette casing 1. Two upwardly extending pins 23 and 24 are provided between the shaft 21 and the tape running path defined by the guide pin or roller 5. A coil spring 25 is disposed around one of the two pins, namely, the pin 23, with one end of the coil spring rockably urging the locking lever 22 towards the side wall 7a of the turnable cover 7 while the other end of the coil spring abuts the other pin 24. The end portion of the locking lever 22, which is bent in the form of the character "L" towards the side wall 7a, is swung into an engaging hole 26 in the turnable cover 7 which is formed in front of a supporting rod 8 of the turnable cover 7 to prevent the cover 7 from being opened.
If a depressing member (not shown) is inserted from outside into an opening 27 in the side wall 7a which is formed between the supporting rod 8 and the engaging hole 26, the depressing member acts against the elastic force of the coil spring to depress one side of a stopper 28 which is provided on one side of the locking lever, and the end portion of the locking lever 22 is swingably displaced to the position indicated by the broken line. Thus, the end portion is disengaged from the engaging hole 26 so that the turnable cover 7 can be opened.
In order to provide the above-described locking mechanism 20 in the cassette, it is necessary to provide a space for arranging the pins 23 and 24 and the coil spring 25 between the locking lever 22 and the tape running path. If this space is in fact provided, the miniaturization of the entire cassette becomes quite difficult. Furthermore, with this construction, if the locking lever is displaced towards the position indicated by the broken line, it may strike the tape T near the above-described guide pin or roller 5 thus damaging the tape T.
Accordingly, an object of the invention is to provide a magnetic tape cassette in which all of the above-described difficulties accompanying the locking mechanism of a conventional magnetic tape cassette are eliminated and which has a relatively low manufacturing cost.